A semiconductor device includes a first substrate, circuit devices disposed on the first substrate, a first interconnection structure electrically connected to the circuit devices, a second substrate disposed on an upper portion of the first interconnection structure, gate electrodes spaced apart from each other and stacked on the second substrate in a direction perpendicular to an upper surface of the second substrate, and channel structures penetrating the gate electrodes, extending perpendicularly to the second substrate, and including a channel layer. The semiconductor device also includes a ground interconnection structure connecting the first substrate and the second substrate, and including an upper via integrated with the second substrate and extending from a lower surface of the second substrate towards the first substrate.